Yuqing Xu

Gated electronic currents modulation and designs of logic gates with single molecular field effect transistors

The electronic transport properties of a gated single 1,3-benzenedithiol molecular device are studied by using nonequilibrium Greens function in combination with density functional theory, which is hoped to complement the experiments. The results show that the external transverse gate electrodes can effectively tune the electronic transport properties of the molecular devices. Negative differential resistance behaviors are observed almost at the same source-drain bias when applied different gate voltages. Mechanisms are proposed for these phenomena. Designs of using one gated molecular device to realize five basic logic gates are also put forward.

Electronic transport properties of indolyl spirooxazine/merooxazine-based light-driven molecular switch: The effect of amino/nitro substituents

Abstract By applying non-equilibrium Greens function formulation combined with first-principles density functional theory, we explore the electronic transport properties of indolinospironaphthoxazine (SO)/indolinomeronaphthoxazine (MO). The results indicate that the MO allows a far larger current than the SO. The substituent group can cause shifts of the energy levels. Higher ON/OFF current ratio can be obtained if either amino or nitro substituent is placed at the position of naphthalene moiety. Our results suggest that such molecular wires can generally display switching function and the efficiency can be increased by adding certain substituent groups to the molecules.

Effect of different electrodes on Fano resonance in molecular devices

By using nonequilibrium Green’s function in combination with density functional theory, we study the electronic transport properties of two typical π-conjugated molecules (dithiol-benzene and C4S2), sandwiched between two metallic electrodes made of different metals. The presence of two different electrodes leads to Fano resonances at certain energy. As a consequence, electronic transport in future molecular electric circuits can be substantially affected when the molecular devices placed between electrodes with different chemical potentials. The Fano line shapes reveal that there is nonresonant channel when two asymmetric electrodes are employed.

Enhanced rectifying performance by asymmetrical gate voltage for BDC20 molecular devices

By applying the asymmetrical gate voltage on the 1,4-bis (fullero[c]pyrrolidin-1-yl) benzene BDC20 molecule, we investigate theoretically its electronic transport properties using the density functional theory and nonequilibrium Greens function formalism for a unimolecule device with metal electrodes. Interestingly, the rectifying characteristic with very high rectification ratio, 91.7 and 24.0, can be obtained when the gate voltage is asymmetrically applied on the BDC20 molecular device. The rectification direction can be tuned by the different gate voltage applying regions. The rectification behavior is understood in terms of the evolution of the transmission spectrum and projected density of states spectrum with applied bias combined with molecular projected self-consistent Hamiltonian states analyses. Our finding implies that to realize and greatly promote rectifying performance of the BDC20 molecule the variable gate voltage applying position might be a key issue.

Rectifying behaviors of an Au/(C20)2/Au molecular device induced by the different positions of gate voltage

The electronic transport properties of a gated Au/(C20)2/Au molecular device are studied using nonequilibrium Greens function in combination with density functional theory. The results show that different applied positions of the external transverse gate voltage can effectively tune the current–voltage (I–V) characteristic of molecular devices. Rectifying behaviors of the device can be realized when the gate voltage is applied asymmetrically on the left C20 molecule, and the rectification directions can also be modulated by the positive or negative value of the gate voltage. These results provide an important theoretical support to experiments and the design of a molecular rectifier.

Electronic transport properties of a dithienylethene-based polymer with different metallic contacts

We have studied the electronic transport behaviors of a dithienylethene-based polymer between two metal surfaces using nonequilibrium Greens functions combined with density functional theory. The present computational results show that the polymer with closed and open configurations really demonstrates switching behavior which confirms the experimental observation. It is also found that the switching behavior depends on the electronic properties of two configurations of polymer instead of the contact modes. The on–off ratios of conductance between the closed and open configurations reach up to two orders of magnitude. Negative differential resistance and rectification phenomena are also observed in such systems.